In general, an oscillator is widely used in various power supply devices or driving devices, and roughly classified into a tuned oscillator and a relaxation oscillator referred to as a charge/discharge oscillator, depending on an implementation method.
The relaxation oscillator, as an oscillator that generates a signal of a desired frequency by using electrical characteristics of a resistor and a capacitor, includes a resistor, a capacitor and a comparator.
Basically, the relaxation oscillator repeats an operation of comparing a charge voltage of the capacitor and a reference voltage by the comparator while charging the capacitor, and discharging and recharging the capacitor when an output logic is changed according to a comparison result.
At this time, an undesired delay occurs in the comparator, and thereby, a frequency error occurs. Recently, circuits which use a feedback loop to compensate for such a delay of the comparator have been suggested. An amplifier is used in such a feedback loop, and a chopping technique is employed to remove low-frequency noise of the amplifier.
In the relaxation amplifier according to the related art, however, a frequency error may be caused by an offset voltage of the comparator and the amplifier, which are generated by a mismatch in process, and a delay which occurs in the comparator.
Furthermore, in the relaxation amplifier according to the related art, the amplifier used for the comparator and the feedback loop may generate low-frequency noise which is responsible for a frequency error and disturbs a stable oscillating operation.